This invention relates to a support structure implant which can be located within a bone cavity to support the bone which defines the cavity. It also relates to an assembly for deploying a stranded support structure implant in a bone cavity.
A cavity might be formed in a bone as a result of disease, or as a result of trauma, or as a result of a surgical procedure. Treatment of the condition can involve supporting the cavity while bone tissue regenerates within the cavity. A filler material can be provided in the cavity. This can be a curable material, for example an acrylate material similar to those used as bone cements to fix joint prosthesis components. It can be a material which stimulates regeneration of bone tissue, for example morcellised bone tissue.
Avascular necrosis (AVN), which is also known as osteonecrosis (ON), ischemic bone necrosis, or aseptic necrosis, results from the temporary or permanent loss of circulation to the bone tissue, and gives rise to localized death of the bone tissue. The loss of proper blood flow can result from trauma, or compromising conditions such as prolonged steroid use, alcohol use, gout diabetes, pancreatitis, venous occlusion, decompression disease, radiation therapy, chemotherapy, and Gaucher's disease.
Osteoporosis is an example of a condition in which bone tissue becomes weakened through a reduction in bone mineral density. Bone microarchitecture becomes disrupted, and the amount and variety of non-collagenous proteins in bone is altered. It can lead to collapse of vertebral structures. It can lead to hip fractures.
Conditions in which a bone is weakened can give rise to severe pain and limitation of movement within a short period, with a 70 to 80% chance of complete collapse of the bone, and of surrounding articulating surfaces when present, after only a few years if the condition is left untreated. In the case of avascular necrosis in the femoral head, it can be necessary for a patient to have joint replacement surgery. In the case of vertebral structures, it can be necessary for the structures to be reinforced to reduce the likelihood of collapse.
Treatments for AVN which focus on salvaging the head of the femur or other bone or joint include core decompression, osteomy, bone grafting, and vascularized fibular grafting.
Wang et al's paper entitled “Superelastic Cage Implantation: A New Technique for Treating Osteonecrosis of the Femoral Head with Middle-Term Follow-ups”, published online in The Journal of Arthroplasty on 10 Oct. 2008, discloses a cage which is formed from 0.5 mm diameter wires. The wires are made from a nickel titanium alloy. The cage is formed from the wires by weaving wires manually. Loops of wire at the poles are held together by lacing a fine wire through the loops. The cage has a 4 mm diameter hole at each pole to allow bone chips to be positioned in the cage. The cage can be positioned in a femoral head through a bore in the femoral neck using an implantation tube.